Electroactive polymers (EAPs) are capable of mechanical actuation induced by an external electric field, and thus afford tremendous promise in emerging technologies ranging from micro air vehicles and flat-panel speakers1; to active video displays, microrobotics and responsive prosthetics.2 Some of the key characteristics required in the development of actuator materials include high strain and strain energy density, high fatigue resistance and reliability.3 
Several classes of materials including single-crystal piezoelectric ceramics4; and single-wall carbon nanotubes5 have been considered as suitable candidates for actuators, but these rigid materials afford relatively low displacement and poor electromechanical coupling in the presence of an electric field.6 While shape memory alloys can generate high forces and displacements, they generally suffer from slow response times, large mechanical hysteresis and short cycle life.7 
Electroactive polymers are attractive due to their low cost, light weight, facile processability,8 favorable power-to-mass ratio and, perhaps most importantly, their potential to emulate biological muscle in terms of resilience, toughness and vibration dampening.9 Examples of EAPs investigated thus far include electrically conductive polymers,10,11 electrostrictive polymers,12 ferroelectric polymers,3,8 dielectric elastomers' and acidic hydrogels.13 Of these, dielectric elastomers exhibit the largest actuation strain upon exposure to an electric field, efficiently coupling input electrical energy and output mechanical energy.14 
The electromechanical response of dielectric EAPs is attributed to the development of a “Maxwell stress” upon application of an external electrical field.15 This Maxwell stress arises in response to electrostatic attraction between two oppositely charged conductive surfaces (or electrodes) in contact with the opposing surfaces of a dielectric elastomer film, and generates a dominant uniaxial stress (σM) given byσM=∈0∈E2  (1)where ∈0 is the permittivity of free space, ∈ corresponds to the dielectric constant of the EAP, and E denotes the applied electric field.1 Since the Maxwell stress acts normal to the film surface, it serves to compress the film along its thickness (z) and stretch the film laterally (along x and y). Repulsive like charges accumulate along both film surfaces and further increase the extent to which the film stretches laterally, as schematically depicted in FIG. 1A.
Three dielectric media that show technological promise derive from homopolymers and include a foamed acrylic adhesive,1,16 polyurethane17 and various silicone elastomers.1,18 The VHB 4910 foamed acrylic adhesive manufactured by 3M Co. (Minneapolis, Minn.) has been reported1 to exhibit the largest actuation strain in this class of materials.
Independent experimental19-21 and theoretical22 studies designed to elucidate the electric field-induced response of another class of macromolecules, microphase-separated block copolymers, have been conducted in an ongoing effort to control nanostructural orientation for various emerging nanotechnologies such as optical waveguides.23 Linear block copolymers consist of two or more dissimilar homopolymers covalently linked together to form a single macromolecule. If the blocks are sufficiently incompatible, these copolymers spontaneously self-organize into a wide variety of (a) periodic nanostructures alone24,25 or in the presence of other species.26-29 Russell and co-workers have established that, due to polarizability differences between the constituent blocks, the lamellar19 and cylindrical21 morphologies of poly(styrene-b-methyl methacrylate) block copolymer thin films can be (re)aligned in a dc electric field. Nanostructural alignment in a block copolymer thin film is likewise achieved by annealing the copolymer in solvent vapor, which alters viscosity, interfacial tension and surface segregation.30 Both strategies have been successfully implemented31 to align the morphologies of bulk poly(styrene-b-isoprene) (SI) diblock copolymers cast from a neutral, volatile solvent.
Solvated block copolymers are likewise of considerable importance in various technologies ranging from personal care products and pharmaceuticals to shock-absorbing media for fiber optics, novel adhesives and sporting goods.26 